This invention relates to a reflective electric lamp, and more particularly to a reflective electric lamp of shield beam type, which is capable of effecting high color rendering.
Conventionally, wide use was made of incandescent and fluorescent lamps as light sources for general illumination. These light sources, however, were not satisfactory as those required to effect high color rendering as in the case of, for example, a light source for illumination of a show window. For example, the fluorescent lamp has the drawback that its warm color and the like are rendered weak although its white color, cold color and the like are rendered intensive. Therefore, attempts have been made to eliminate such drawback of the fluorescent lamp by improving, for example, the compositions of the phosphor. A satisfactory result, however, has not yet been obtained. Further, the incandescent lamp has the drawback that, since it emits yellowish light components, its whitish color is rendered weak. For the purpose of removing such drawback is practically used an incandescent lamp having a bulb formed of glass material containing neodymium. The glass material containing neodymium selectively absorbs lights having a wavelength 580 nm and around 580 nm, i.e., yellowish lights. If, therefore, the bulb of an incandescent lamp is formed of such glass material, it will absorb yellowish lights numerously contained in the lights emitted from the incandescent lamp. Accordingly, all colors of articles illuminated by the lights emitted from the lamp, including warm colors, cold colors, whitish colors, etc., look very clear. This means that such incandescent lamp indicates a high color rendering. The incandescent lamp, therefore, suits illuminating fresh foods such as fish, meats, and vegetables and colorful cloths.
The glass material containing neodymium, however, has the property of absorbing not only the above-mentioned yellowish lights but also the lights whose wavelengths fall on and within the area near the border of wavelength between red and near infrared lights. The bulb formed of such glass material, therefore, is inconveniently more allowed to heat than a bulb formed of usual glass material. Particularly, the lamp for illumination of fresh foods is required to make the freshness of the foods inpressive. This means that a high intensity of illumination is demanded of such lamp. This results in a large light flux of the bulb per unit area. This causes an excessive increase in the temperature of the bulb to cause evolution of gases from it. This shortens the life of the bulb. In order to prevent such increase in the bulb temperature, limitation must be imposed upon the containing amount of neodymium. This, however, becomes a barrier in achieving a high color rendering. Further, neodymium is nowadays very expensive and the lamp using glass material containing such expensive neodymium is also expensive. This is a barrier in making the use of such lamp wider.